The present invention relates to a process for separation of hafnium tetrachloride from zirconium tetrachloride and electrode which produces zirconium tetrachloride with a low hafnium content suitable for a raw material of the production of zirconium metal of reactor grade and hafnium tetrachloride with a high hafnium content suitable for a raw material of hafnium metal with high efficiency respectively.
Zirconium ore contains generally about 2.about.4 wt % of hafnium. Conventionally in commercial processes for separation of hafnium from zirconium there are a solvent extraction process which uses zirconium tetrachloride as a starting material and hexon as a solvent (J. W. Ramsey, W. K. Whitson Jr.: Production of zirconium at Y-12, AEC Report Y-817, October 12, 1951) and a distillation process (Paul Benson, Jean Guerin, Pierre Brun, Michel Bakes: French Patent No. 7340395, Japanese Patent Publication No. 20279 of 1978, Pierre Brun, Jean Guerin: Japanese Patent Provisional Publication No. 184732 of 1984).
In the former the running cost is high owing to its low recovery of solvent and chemicals used. In the latter the running cost is low, however, a huge distiller is required and its maintenance cost is high. As a patent somewhat related to the present invention, there is a process in which zirconium tetrachloride is reduced to trichloride by the use of a reducing agent to be separated by distillation (I. E. Newnham: U.S. Pat. No. 2,791,485, May 7, 1957), but this process is not yet commercialized owing to the difficulty in separation of the reducing agent.
On the other hand, as mentioned above, zirconium ore contains about 2.about.4 wt % of hafnium. As hafnium tetrachloride is slightly more stable than zirconium tetrachloride for the chlorination reaction of both oxides, the concentration of hafnium tetrachloride in the chlorides is almost the same as that of the ore. Zirconium tetrachloride containing hafnium tetrachloride in natural retio is a starting material for production of zirconium and hafnium metals. As the thermal neutron absorption cross section of hafnium is high, a hafnium content in zirconium used for a reactor must be less than 100 ppm. Besides, hafnium is an excellent control material for a reactor because of its high absorption of neutron.